Diamonds increase efficiency

2017-03-14

Diamonds increase efficiency

Mario Pichler at the finishing line in just a few mouse clicks. A table that appears rather complex to outsiders is displayed on the screen. This table comprises information regarding orders for consumables that are subject to wear during the production of high-precision engine components on the factory floor next door and are regularly replaced. Pichler, Head of Strategic Metrology at Pankl Racing, points to a line in the table in which a ZEISS stylus is mentioned. "We installed it on 17 November 2015." Today, on 26 July 2016, the stylus is obviously still in operation, as there have been no entries since then.
If Mario Pichler had shown the same table a year ago, it would have told a different story altogether. Substantial numbers of styli would have been listed in the Kanban system, which documents all material flows in the factory. A new one per day was not a rare occurrence at the time. On 17 November 2015, something must have happened here which drastically changed the manufacturer's production of high-performance engine components – including connecting rods for almost all Formula 1 teams. The cursory line in the table marks the replacement of the previously used silicone nitride styli by a diamond stylus in a ZEISS PRISMO coordinate measuring machine. Since its replacement, this stylus has been running perfectly up to now, and there is no end in sight. "We have not detected any signs of wear whatsoever", says Pichler, in praise of the new stylus. Things were different with the old styli. They wore quickly, which had a detrimental effect on measuring accuracy.

Skeptical for a long time

Mario Pichler describes himself as thorough, determined and with an enthusiasm for technology. His goal is automation and making procedures easier; there is no limit to his conceptual ideas. It is therefore all the more astonishing that it took six years for the 33-year old to be convinced by diamond styli. "I do admit that I was sceptical for a long time." Perhaps this was due to the fact that the diamond styli were a solution to a problem that had not been pressing at Pankl in the past. This is because the tolerances of engine components used to be determined by discrete-point measurement. This means that the stylus of the coordinate measuring machine approaches a point on the component, records the measured value, returns and moves to another point. This has some disadvantages: If the measurement is to be of short duration, only a few points can be measured, perhaps a couple of dozen, which has a negative effect on accuracy. If the measurement needs to be more accurate, more measuring points are required and therefore considerably more time.
This strategy works as long as the number of parts to be tested is small and the requirements for accuracy are moderate. But this changed at Pankl. Customer requirements for precision increased continuously. Above all, the Formula 1 engine manufacturers continue to tighten the screw with regard to precision. The connecting rods, which transfer the power from the piston to the rotating crankshaft, are an example of this: The connecting rods for racing engines are milled from one piece, receive multiple coatings and are of such a slim design that the engine does not need to move one gramme more than is absolutely necessary. Since the engineers come close to the limits of what is technically feasible, even the slightest production tolerances can pose a risk for the service life of the engines. Even if the forged connecting rods for series engines have to withstand far lower peak loads, they still need to last for several hundred thousand kilometers. The demands of the automotive manufacturers have increased accordingly.

Scanning with obstacles

Pankl came to a point where the quantity and precision of the components could no longer be obtained with individual measurements in the production. Some of the coordinate measuring machines were therefore converted to scanning. In this case, the stylus always remains in contact with the component and moves along its surface. The number of measuring points increases. But what about the precision?
Unfortunately not, says Pichler, pointing to a connecting rod for a racing engine. It has a defined structure on the inside where it is later mounted on the crankshaft and is therefore slightly rough. If a silicone nitride or ruby stylus moves across it, a little material is removed: The stylus sphere becomes imbalanced. Each day the sphere is worn by up to one micrometer – too much for customers used to high precision.

Calibrating twice a day

Pankl managed to get a grip on the deviations but at a high price. Henceforth, each stylus was calibrated twice a day with a measurement standard, which caused a downtime of 15 minutes in each case. In addition to this, the measurement engineers tried various stylus variants: Styli with a silicone nitride sphere from another manufacturer (Pichler: "No improvement") or with ruby ("Even more problems").
This went on for seven years. During the course of time, procedures established themselves, Pankl got a grip on the measurement tolerances and the costs for the silicone nitride styli, which had to be replaced every few days, were acceptable at 70 euros per stylus system. Nevertheless, Pichler became curious last year when the field service of ZEISS announced new styli with a diamond coating. These would only cost just over half the price of a full diamond stylus. Pichler's interest was aroused; he ordered a stylus – at first the expensive full diamond version on loan – for one of the two ZEISS PRISMOs, which are used for the final check of connecting rods. As mentioned at the beginning, the stylus went into service on 17 November 2015 – and is still working with the same precision to this day. All connecting rods for racing engines undergo their final check here. A scan only takes three minutes, but many more measured values are obtained than was previously the case with the discrete-point measurements; reliability is therefore higher.

Further diamond styli planned

One of the new diamond-coated styli is now also in use at Pankl. Another measuring machine operating in the intermediate checking process is now equipped with a full diamond stylus. As the machine is mainly operated by production staff, occasional collisions occur between the stylus and the workpiece. However, as these are extremely rare and only occur at a low travel speed, Mario Pichler is still prepared to take the risk of using the expensive stylus. If a full diamond sphere breaks off – which cannot be completely avoided in the rough operating conditions – the ZEISS technicians solder the sphere back on again.
Things will remain the same for the time being in the case of the five measuring machines ZEISS DuraMax, two CONTURA and the third PRISMO, where scanning does not take place. Yet. Because Pichler, who says that changing over to the diamond-coated and full diamond styli "really paid off", is already thinking ahead, and is starting to examine the use of these styli in gearbox production.

Short profile
Pankl Racing Systems
Pankl Racing Systems AG with its headquarters in Kapfenberg, Austria, develops, produces and sells engine and drive systems as well as chassis components for racing sports, luxury cars and helicopters. Pankl produced the first connecting rods for motor sports as early as 1985. Today, the Racing Division is a market-leading supplier of engine and drive systems. The engine systems are manufactured in Bruck an der Mur, Austria and in Irvine, California, and the drive systems in Kapfenberg, Austria and Bicester, Great Britain. Pankl employs a workforce of about 1,300 worldwide.

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